1

Whilst on holiday in Iceland, I forgot to buy a ND filter, which didn't allow me to take long exposure shots of waterfalls. I have a few images that I would have preferred to expose for longer but couldn't due to the abundance of light.

Is there any way I can perhaps make my photos look slightly longer exposed? I have looked at tutorials on youtube, and they recommend using a motion-blur filter, I have tried this, but it doesn't give such a great result. Does anyone know anymore techniques I could use?

All answers appreciated!

  • My personal opinion is not to bother, it wont look right without a lot of skill/time, and a crisp water shot will look better than a cheesy photoshop attempt. Next time you're stuck without an ND filter, stop down to get the shutter time as slow as you can and take a long series of images and stack them when you get home. – Matt Grum Jun 19 '14 at 11:05
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    @MattGrum: I dunno. Photoshop is awfully powerful in itself, and in the right hands, it is capable of wonders. The new motion blur path feature in Photoshop CC 2014 would help sell a faux water blur in a rocky stream by letting you shape the blur over the rocks. If you're not on the CC train, some judicious liquification should do the trick. – Warren Young Jun 30 '14 at 23:28
4

I was going to say that it isn't possible, but I did figure out at least one way to sort of do it, at least for some images of some waterfalls, with somewhat acceptable results sometimes. Caveat emptor.

The trick I came up with relies on the fact that, in a typical picture of a waterfall, the water looks white while the background is mostly dark. Thus, by using a technique similar to exposure fusion, we can blur the water while keeping the background sharp. Also, as long as the water is all mostly moving in the same direction (down), we can more or less get away with a simple linear blur — don't try this on a picture of churning rapids.

For a demonstration, let me use this public domain picture of the Pacheco Waterfall in Venezuela by Hellen Perrone at Wikimedia Commons, taken with a shutter speed of about 1/200 s:

    Pacheco Waterfall in Venezuela by Hellen Perrone at Wikimedia Commons
(Click the images to view them at full size.)

The first step is make a copy of the image on a new layer, and to cut away anything that is (close to) white except the waterfall. In this photo, that mostly means the sky:

    Step 1: Cut away the sky, and everything else white that isn't waterfall
(Here, as in the images below, transparent areas are shown as black.)

Next comes the trick: add a layer mask to the new layer, and set it to a grayscale copy of the layer. This effectively makes the dark (non-waterfall) parts of the layer transparent, while leaving the light (waterfall) parts opaque:

    Step 2: Add layer mask, set it to grayscale copy of layer
(Again, the layer is shown on a black background. Here's a small transparent PNG version, if you prefer.)

To better separate the waterfall and non-waterfall parts, we need to increase the contrast of the mask. To do that, I selected the mask and adjusted its color levels using a strong S curve:

    Step 3: Increase mask contrast   Screenshot of curves adjustment
(Here's another transparent PNG for those who like them better.)

After applying the layer mask (to merge it into the alpha channel), we're ready to add some motion blur. Here, I used a linear blur with a 50px blur length (quite large, to make it obvious even at small sizes) and an angle of 265 degrees (5 degrees off straight down):

    Step 4: Add motion blur
(And here's a transparent PNG version of this step too.)

Replacing the black background with the original photo, the combined image looks like this:

    Step 5: Place masked and blurred layer on top of original

Finally, a bit of manual erasing fixes a few inappropriately blurred spots, producing this result:

    Final result: Waterfall with fake long exposure

  • +1, but you might add some more detail on the "Replacing the black background with the original photo" step. I'd do that with a blend mode (lighten?) but you might have another technique. – Warren Young Jun 18 '14 at 23:55
  • @WarrenYoung: I just removed the solid black layer that I had added between the edited layer and the original. The actual blurred layer is semitransparent; I'm just using a black background because JPEG doesn't do transparency (and it'd look awful here on the light page background anyway). I suppose I could upload it as a transparent PNG, but it'd be huge at full size. – Ilmari Karonen Jun 18 '14 at 23:58
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Motion blur is the right answer. Perhaps all that's required here is a bit of technique. If you post an image for us to play with, I think one of us might get better results than you did, and can then tell you how they did it.

In the end, what you're asking for here is for someone to create time. You're asking us how you can invent another second or so of the time that occurred after the camera's shutter closed. A good photorealistic painter can create such things, and there are clever algorithms for adding motion to a still photograph, but these things require a lot of skill and work, because it's all pure invention.

We see the same problem in computer generated 3D graphics. If you render an animation at a steady 30 fps, you don't get 1/30 sec exposures in each frame. If you did, moving objects would have some motion blur. Instead, a typical 3D rendering program gives you an instantaneous "exposure" for each frame, which is why a lot of 3D animation looks super-crisp and unreal. To fake the motion blur, you have to render the positions of the moving objects in the scene at several intermediate points along their motion path, then blend them together somehow. So, instead of rendering 30 fps, you might effectively have to render 300 fps, then blur that down to 30 fps.

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I would have taken many pictures on a tripod, aligned them (e.g. using the align_image_stack program) and then taken the average of the pictures. This can yield better results than using an ND filter as aligning the images will correct for slight movements of the camera orientation, e.g. due to wind.

  • Again, not really helpful for the OP who has only one photo. – Philip Kendall Apr 15 '15 at 16:53
  • But the reason why the OP only has one photo is because he/she thought that without an ND filter you cannot do anything while taking the pictures and only post processing options on a single picture is available. The OP asked the question a long time ago, the people searching for advice when they don't have an ND filter may get this question in their search results, so something must be said about what you can do if you don't have an ND filter handy. – Count Iblis Apr 15 '15 at 17:00
  • And that would be a good answer to a general "how can I simulate a long exposure without an ND filter?" question, but not to this question which is explicitly about doing it in Photoshop. – Philip Kendall Apr 15 '15 at 20:53
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If you have Photoshop CS6 Extended (or CC) you can do the following:

Ideally:

(1) Shoot a burst of images of the moving water subject. For example in my first ever try (see below) I shot 15 images at 1/50th and f8 (freehand with a stabilised lens) of a Waterfall. (BTW I actually came here looking for an answer on doing this, but am ending up providing one instead, with a bit of a gap to try stuff in-between).

But you can also try:

(1) If you have several images shot from the same position in the same direction (you may need to even out the exposure if some are lighter/darker) and at the same focal length.

(2) In Photoshop do File->Scripts->Statistics...

(3) In the resulting dialogue select your files, Select "Mean" in the drop-down and tick "Attempt to Automatically Align Source Images".

(4) Wait for it all to happen

(5) Crop to suit - note the example below is uncropped to show what you get.

Example: Waterfall - 15 images at 1/50th merged

All done :-)

Cheers

John

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    As with the other answers, the OP has only one image. A solution which starts with "shoot a stack of images" doesn't work. – Philip Kendall Jun 19 '15 at 13:56
  • Probably true, but he doesn't say that specifically and if he shot several images from the same position he could try applying this. I will update the answer to make this point clearer. – Dr_Jon Jun 19 '15 at 20:37

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